In X-ray CT systems, X-rays are used to image internal structure and features of a region of a subject or an object. The terms “subject” and “object” shall include anything capable of being imaged. The imaging is performed by an X-ray CT system, which images internal structure and features of a plurality of thin planar slices or a 3D volume of a region of an object using X-rays. For medical applications, the imaging objects include human bodies.
An X-ray CT system generally comprises an X-ray source that provides a cone-shaped X-ray beam and an array of closely spaced X-ray detectors that face the X-ray source. The X-ray source and array of detectors are mounted in a gantry so that a patient being imaged with the CT system, generally lying on an appropriate support couch, can be positioned within the gantry between the X-ray source and the array of detectors. The gantry and couch are moveable relative to each other so that the X-ray source and detector array can be positioned axially at desired locations along the patient's body.
The gantry comprises a stationary structure referred to as a stator and a rotary element referred to as a rotor, which is mounted to the stator so that the rotor is rotatable about the axial direction. In third generation CT systems, the X-ray source and detectors are mounted on the rotor. Angular positions of the rotor about the axial direction are controllable so that the X-ray source can be positioned at desired angles, referred to as view angles, around a patient's body.
To image a slice in a region of a patient's body, the X-ray source is positioned at the axial position of the slice and the X-ray source is rotated around the slice to illuminate the slice with X-rays from a plurality of different view angles. At each view angle, detectors in the array of detectors generate signals responsive to the intensity of X-rays from the source that pass through the slice. The signals are processed to determine amounts, by which X-rays from the X-ray source are attenuated over various path lengths through the slice that the X-rays traverse, in passing though the slice from the X-ray source to the detectors. The amounts, by which the X-rays are attenuated, are used to determine an X-ray absorption coefficient of materials in the slice as a function of position in the slice. The absorption coefficient is used to generate an image of the slice and identify compositions and densities of tissues in the slice.
The X-ray detectors comprised in a detector array of CT system are generally packaged in a plurality of modules, hereinafter referred to as CT detector-modules, each of which comprises a plurality of X-ray detectors. Most modern CT systems are multi-slice CT systems designed to simultaneously image a plurality of slices of a patient. The X-ray detectors in each CT detector-module of a multi-slice scanner are arranged in a rectangular matrix of rows and columns. The X-ray detector matrices of any two CT detector-modules in a CT system are substantially identical and comprise a same number of rows of detectors and a same number of columns of detectors. The modules are positioned one adjacent to and contiguous with the other in a closely packed array with their rows of detectors aligned end to end so that the X-ray detectors form a plurality of long parallel rows of X-ray detectors.
A multi-slice X-ray CT system is usually named or featured by the maximum number of slices that it can simultaneously image, for example, an 8-slice CT system means that it can simultaneously image at most 8 slices; a 16-slice CT system can simultaneously image at most 16 slices.
The X-ray detectors in each long row of detectors lie on an arc of a circle having its center located at a focal point of the CT system's X-ray source, and the design of these detectors is specifically determined by the radius of the circle, which is hereinafter referred to as focusing distance. The design of X-ray detectors placed on the arc of one focusing distance of one CT system cannot therefore be used on another CT system of a different focusing distance.
X-ray detectors typically include a collimator having a plurality of anti-scatter plates for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electric charges therefrom. The anti-scatter plates of a collimator are aligned and bounded with the elements of the scintillator arrays to very tight and exact tolerances. This alignment and bounding of the plurality of elements of the scintillator array and the anti-scatter plates of the collimator can be a time consuming and a labor intensive process.
Electronic components for processing analog signals from the X-ray detectors in a CT detector-module are usually located at positions removed from the detector module. Each detector in a detector module is connected to the module's electronic processing components via a cable over which analog signals from the detector are transmitted to the processing electronics. Because the electric charges produced by the photodiodes are extremely small, the cables carrying these small charges are very susceptible to interferences, resulting in artifacts in reconstructed CT images; the longer the cables are, the more interferences they are exposed to.